I'm going to use Drupal terminology here, but the same basic weakness applies to ... pretty much every CMS currently in use across the think tank sector.
This is where things get a bit risky. I’ve chosen to use entity here to avoid the controversy around content type. But of course entity has a technical meaning in Drupal—one that is broader than the Drupal meaning of content type. For example, an image plus its associated metadata is a Drupal entity, but it’s not a content type. Here I’ll use entity to refer to logically connected independent sets of attributes and nested entity to refer to logically connected sets of attributes that are not meant to be consumed as independent things.
The standard field type for relating two pieces of content (in this case, an article containing a quotation and the source of that quotation) is an entity reference field. But notice that it's an entity reference field, not an entity relationship field. That's a deliberate naming choice. It means that entity references give us something like this: